Please document how to handle errors

[joshtriplett]

With standard iterators, it's possible to call map with a function that returns a Result<T, E>, then collect into a Result<Vec<T>, E>. I'd like to do something similar with a ParallelStream, but it looks like the collect method only supports collecting into a Vec, not a Result.

Would you consider providing some documentation on how to handle errors that occur in one of the parallel function calls?